U.S. patent number 7,083,506 [Application Number 10/895,395] was granted by the patent office on 2006-08-01 for polishing apparatus.
This patent grant is currently assigned to Ebara Corporation. Invention is credited to Hideo Aizawa, Soichi Isobe, Hiroomi Torii.
United States Patent |
7,083,506 |
Torii , et al. |
August 1, 2006 |
**Please see images for:
( Certificate of Correction ) ** |
Polishing apparatus
Abstract
A polishing apparatus comprises a polishing table having a
polishing surface thereon, a top ring for pressing a workpiece to
be polished against the polishing surface, and a dresser for
dressing the polishing surface on the polishing table. The dresser
comprises a dressing element provided on a surface of the dresser
for dressing the polishing surface by sliding contact with the
polishing surface, and an ejection nozzle provided on the surface
of the dresser for ejecting a fluid supplied from a fluid source
toward the polishing surface.
Inventors: |
Torii; Hiroomi (Tokyo,
JP), Aizawa; Hideo (Tokyo, JP), Isobe;
Soichi (Tokyo, JP) |
Assignee: |
Ebara Corporation (Tokyo,
JP)
|
Family
ID: |
18777219 |
Appl.
No.: |
10/895,395 |
Filed: |
July 21, 2004 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20040259486 A1 |
Dec 23, 2004 |
|
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
09962330 |
Sep 26, 2001 |
6783445 |
|
|
|
Foreign Application Priority Data
|
|
|
|
|
Sep 27, 2000 [JP] |
|
|
2000-294666 |
|
Current U.S.
Class: |
451/285; 451/443;
451/444 |
Current CPC
Class: |
B24B
37/04 (20130101); B24B 53/013 (20130101); B24B
53/017 (20130101); B24B 53/12 (20130101); B24B
57/02 (20130101) |
Current International
Class: |
B24B
7/00 (20060101) |
Field of
Search: |
;451/443,444,285-289,56 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Tatsuo Inoue et al., U.S. Appl. No. 09/790,976, filed Feb. 23,
2001. cited by other.
|
Primary Examiner: Rachuba; M.
Attorney, Agent or Firm: Wenderoth, Lind & Ponack
Parent Case Text
This application is a divisional of U.S. application Ser. No.
09/962,330, filed Sep. 26, 2001 now U.S. Pat. No. 6,783,445.
Claims
What is claimed is:
1. A polishing apparatus comprising: a polishing table having a
polishing surface thereon; a top ring for pressing a workpiece to
be polished against said polishing surface; and a dresser for
dressing said polishing surface on the polishing table, said
dresser including (i) a dressing element provided on a surface of
said dresser for dressing said polishing surface by sliding contact
with said polishing surface, and (ii) an ejection nozzle provided
on the surface of said dresser for ejecting a mixture, of a fluid
supplied from a fluid source and a gas supplied from a gas source,
toward said polishing surface, said ejection nozzle being directed
toward an outer circumferential edge of said dressing element so as
to eject the mixture of the fluid and the gas toward the outer
circumferential edge of said dressing element, wherein said
dressing element is annularly disposed on the surface of said
dresser, and said ejection nozzle is disposed in an area surrounded
by said dressing element.
2. The polishing apparatus according to claim 1, wherein: said
dressing element has a fluid flow hole defined therethrough for
flowing the mixture of the fluid and the gas to a lower surface of
said dressing element, and a fluid ejection slot defined in the
lower surface of said dressing element; and said fluid ejection
slot is extended from said fluid flow hole to an the outer
circumferential edge of said dressing element.
3. The polishing apparatus according to claim 2, wherein said
dresser further includes a rotary joint provided in a passage for
supplying the mixture of the fluid and the gas to said ejection
nozzle.
4. The polishing apparatus according to claim 1, wherein said
dresser further includes a rotary joint provided in a passage for
supplying the mixture of the fluid and the gas to said ejection
nozzle.
5. The polishing apparatus according to claim 1, wherein said
dressing element comprises plural dressing members arranged in an
annular configuration.
6. The polishing apparatus according to claim 5, wherein: each one
of said plural dressing members has a fluid flow hole defined
therethrough for flowing the mixture of the fluid and the gas to a
lower surface of said each one of said plural dressing members, and
a fluid ejection slot defined in the lower surface of said each one
of said plural dressing members; and said fluid ejection slot is
extended from said fluid flow hole to an outer edge of said each
one of said plural dressing members.
7. The polishing apparatus according to claim 6, wherein said
dresser further includes a rotary joint provided in a passage for
supplying the mixture of the fluid and the gas to said ejection
nozzle.
8. The polishing apparatus according to claim 5, wherein said
dresser further includes a rotary joint provided in a passage for
supplying the mixture of the fluid and the gas to said ejection
nozzle.
9. A dresser for dressing a polishing surface on a polishing table,
comprising: a dressing element provided on a surface of said
dresser for dressing the polishing surface by sliding contact with
the polishing surface; and an ejection nozzle provided on the
surface of said dresser for ejecting a mixture, of a fluid supplied
from a fluid source and a gas supplied from a gas source, toward
the polishing surface, said ejection nozzle being directed toward
an outer circumferential edge of said dressing element so as to
eject the mixture of the fluid and the gas toward the outer
circumferential edge of said dressing element, wherein said
dressing element is annularly disposed on the surface of said
dresser, and said ejection nozzle is disposed in an area surrounded
by said dressing element.
10. The dresser according to claim 9, wherein: said dressing
element has a fluid flow hole defined therethrough for flowing the
mixture of the fluid and the gas to a lower surface of said
dressing element, and a fluid ejection slot defined in the lower
surface of said dressing element; and said fluid ejection slot is
extended from said fluid flow hole to the outer circumferential
edge of said dressing element.
11. The dresser according to claim 10, further comprising: a rotary
joint provided in a passage for supplying the mixture of the fluid
and the gas to said ejection nozzle.
12. The dresser according to claim 9, further comprising: a rotary
joint provided in a passage for supplying the mixture of the fluid
and the gas to said ejection nozzle.
13. The dresser according to claim 9, wherein said dressing element
comprises plural dressing members arranged in an annular
configuration.
14. The dresser according to claim 13, wherein: each one of said
plural dressing members has a fluid flow hole defined therethrough
for flowing the mixture of the fluid and the gas to a lower surface
of said each one of said plural dressing members; and said fluid
ejection slot is extended from said fluid flow hole to an outer
edge of said each one of said plural dressing members.
15. The dresser according to claim 14, further comprising: a rotary
joint provided in a passage for supplying the mixture of the fluid
and the gas to said ejection nozzle.
16. The dresser according to claim 13, further comprising: a rotary
joint provided in a passage for supplying the mixture of the fluid
and the gas to said ejection nozzle.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polishing apparatus for
polishing a workpiece to be polished, and more particularly to a
polishing apparatus for polishing a workpiece having a thin film
formed thereon, such as a semiconductor wafer, to a flat mirror
finish.
2. Description of the Related Art
As semiconductor devices have become more highly integrated in
recent years, circuit interconnections have become finer and
distances between these circuit interconnections become smaller. In
case of photolithography which can form interconnections that are
at most 0.5 .mu.m wide, it is required that surfaces on which
pattern images are to be focused by a stepper should be as flat as
possible because a depth of focus of an optical system is
relatively small. A polishing apparatus for performing chemical
mechanical polishing (CMP) has been used for planarizing
semiconductor wafer.
This type of polishing apparatus comprises, as shown in FIG. 1, a
polishing table 302 having a polishing cloth (polishing pad) 300
attached thereon and constituting a polishing surface, and a top
ring 304 for holding a substrate W as a workpiece to be polished,
such as a semiconductor wafer, in such a manner that a surface to
be polished faces the polishing cloth 300. A semiconductor wafer W
is polished by this polishing apparatus as follows: The polishing
table 302 and the top ring 304 are independently rotated, and,
while a polishing liquid is supplied 25 from a polishing liquid
nozzle 306 provided above the polishing table 302, the
semiconductor wafer W is pressed against the polishing cloth 300 on
the polishing table 302 at a predetermined pressure by the top ring
304. For example, a suspension of fine polishing particles of
silica or the like in an alkali solution is used as the polishing
liquid supplied from the polishing liquid nozzle 306. Thus, the
semiconductor wafer W is polished to a flat mirror finish by a
combined effect of a chemical polishing effect attained by the
alkali and a mechanical polishing effect attained by the polishing
particles.
When the semiconductor wafer W is brought into contact with the
polishing cloth 300, and the polishing table 302 is rotated to
perform polishing, a polishing liquid or ground-off particles of
semiconductor material are attached to the polishing cloth 300,
resulting in a change in properties of the polishing cloth 300 and
deterioration in polishing performance. Therefore, if an identical
polishing cloth 300 is repeatedly used for polishing semiconductor
wafers W, problems such as lowered polishing rate and uneven
polishing are caused. In order to overcome such problems, a dresser
308 is provided in the polishing apparatus, and the polishing cloth
300 is dressed by the dresser 308 at a time of replacement of a
semiconductor wafer W to be polished, for example. During a
dressing process, while a dressing element attached to a lower
surface of the dresser 308 is pressed against the polishing cloth
300 on the polishing table 302, the polishing table 302 and the
dresser 308 are independently rotated to remove the polishing
liquid and the ground-off particles of the semiconductor material
which are attached to the polishing surface and to flatten and
dress the polishing surface in its entirety, whereby the polishing
surface is regenerated. This dressing process is also referred to
as a conditioning process.
During the dressing process, a portion of the dressing element
brought into sliding contact with the polishing surface may come
off the lower surface of the dresser and remain on the polishing
surface in some cases. If the portion of the dressing element that
has come off the lower surface of the dresser remains on the
polishing surface, then a surface of a subsequent semiconductor
wafer to be polished may be scratched by this portion of the
dressing element.
For example, in the case of a diamond dresser, which comprises a
dressing element constituted by particles such as diamond particles
electrodeposited on a lower surface of a dresser, in order to
reduce a number of diamond particles which come off the dressing
element, it has been attempted to reduce a number of suspended
particles present on the lower surface of the dressing element by
performing an initial run-in or positioning the diamond particles
at increased intervals. However, it is highly difficult to
completely eliminate diamond particles from coming off the dressing
element.
After a semiconductor wafer is polished by the top ring, polishing
liquid used during the polishing process and ground-off particles
of semiconductor material may possibly remain on the polishing
surface of the polishing cloth. Since these remaining polishing
liquid and ground-off particles tend to scratch a surface of a
semiconductor wafer, it is necessary to remove them before a
subsequent polishing process is performed.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a
polishing apparatus which can reliably remove a portion of a
dressing element that has come off the dressing element, a
polishing liquid, and ground-off particles of a workpiece material,
with ease, and can increase quality of polishing of a
workpiece.
In order to attain the above object, according to a first aspect of
the present invention, there is provided a polishing apparatus
comprising: a polishing table having a polishing surface thereon; a
top ring for pressing a workpiece to be polished against the
polishing surface; a dresser for dressing the polishing surface on
the polishing table; a dressing element provided on a surface of
the dresser for dressing the polishing surface by sliding contact
with the polishing surface; and an ejection nozzle provided on the
surface of the dresser for ejecting a fluid supplied from a fluid
source toward the polishing surface.
With the above arrangement, a portion of the dressing element that
has come off the dressing element during a dressing process, a
polishing liquid, and ground-off particles of a workpiece material,
are scattered toward an exterior of the dresser by fluid ejected
from the ejection nozzle. Thus, the portion of the dressing
element, the polishing liquid, and the ground-off particles, which
remain on the polishing surface to cause a scratch, can effectively
be removed from the polishing surface. Therefore, quality of
polishing of a workpiece can be increased.
According to a second aspect of the present invention, there is
provided a polishing apparatus comprising: a polishing table having
a polishing surface thereon; a top ring for pressing a workpiece to
be polished against the polishing surface; a dresser for dressing
the polishing surface on the polishing table; a dressing element
provided on a surface of the dresser for dressing the polishing
surface by sliding contact with the polishing surface; and an
ejection nozzle provided on the surface of the dresser for ejecting
a mixture of a liquid supplied from a liquid source and a gas
supplied from a gas source toward the polishing surface.
With the above arrangement, a polishing liquid and ground-off
particles of a workpiece material which have fallen into recesses
in the polishing surface can be blown away from the recesses by the
gas contained in the mixture, and, further, can be washed away by
the liquid. Thus, the polishing surface can effectively be
cleaned.
Preferably, a dressing element is annularly disposed on the lower
surface of the dresser, and the ejection nozzle is disposed inside
of the annularly disposed dressing element.
According to a preferred aspect of the present invention, the
dressing element has a fluid flow hole defined therethrough for
flowing fluid from the fluid source to a lower surface of the
dressing element, and a fluid ejection slot defined in a lower
surface of the dressing element; and the fluid ejection slot is
extended from the fluid flow hole to an outer circumferential edge
of the dressing element.
With the above arrangement, fluid strongly flows out of the dresser
under centrifugal forces due to rotation of the dresser. Therefore,
a polishing surface can effectively be cleaned.
Preferably, the fluid ejection slot is extended toward an outer
circumferential edge of the dresser. This arrangement can
effectively increase a force of flow of fluid. Hence, an effect of
cleaning of a polishing surface can be improved.
The above and other objects, features, and advantages of the
present invention will be apparent from the following description
when taken in conjunction with the accompanying drawings which
illustrates preferred embodiments of the present invention by way
of example.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a vertical cross-sectional view showing a conventional
polishing apparatus;
FIG. 2 is a plan view showing a polishing apparatus according to an
embodiment of the present invention;
FIG. 3 is a perspective view showing the polishing apparatus shown
in FIG. 2;
FIG. 4 is a vertical cross-sectional view showing a polishing
section of the polishing apparatus shown in FIGS. 2 and 3;
FIG. 5 is a schematic view showing a piping system of a dressing
unit in the polishing section shown in FIG. 4;
FIG. 6 is a bottom view showing a dresser in the dressing unit
shown in FIG. 5;
FIG. 7A is an enlarged view showing a dressing element of the
dresser shown in FIG. 6;
FIG. 7B is a cross-sectional view taken along a line H--H of FIG.
7A; and
FIG. 8 is an enlarged view showing a dressing element according to
another embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A polishing apparatus according to an embodiment of the present
invention will be described below with reference to FIGS. 2 through
7B.
FIG. 2 is a plan view showing a polishing apparatus according to an
embodiment of the present invention, and FIG. 3 is a perspective
view showing the polishing apparatus shown in FIG. 2. As shown in
FIGS. 2 and 3, in the polishing apparatus according to this
embodiment, a pair of polishing sections 1a, 1b is disposed on one
side of a space on a floor having a rectangular shape, so as to
laterally face each other. A pair of load/unload units for placing
thereon cassettes 2a, 2b for accommodating semiconductor wafers
therein is disposed on another side of the space. Two transfer
robots 4a, 4b for transferring a semiconductor wafer are disposed
on a line connecting the polishing sections 1a, 1b to the
load/unload units to constitute a transfer line. Two inverters 5, 6
are disposed on each side of the transfer line, and two sets of
cleaning units 7a, 7b and 8a, 8b are disposed on each side of the
transfer line. The inverter 5 is interposed between the cleaning
units 7a and 8a, and the inverter 6 is interposed between the
cleaning units 7b and 8b.
The two polishing sections 1a, 1b have basically identical
specifications relative to each other, and are positioned
symmetrically with respect to the transfer line. Each of the
polishing sections 1a, 1b comprises a polishing table 11 having a
polishing cloth attached to an upper surface thereof, a top ring
unit 12 for holding a semiconductor wafer W, as a workpiece to be
polished, by vacuum suction and pressing the semiconductor wafer W
against the polishing table 11 to polish the semiconductor wafer W,
and a dressing unit 13 for dressing the polishing cloth on the
polishing table 11. Pushers 14 for receiving a semiconductor wafer
W from the top ring unit 12 and transferring the semiconductor
wafer W to the top ring unit 12 are provided near the transfer line
in each of the polishing sections 1a, 1b.
A polishing surface is constituted by an upper surface of the
polishing cloth. The polishing surface may be constituted by a
fixed abrasive pad or a grinding stone. The polishing cloth can be
made of elastic polyurethane foam or a non-woven fabric. The
grinding stone comprises abrasive particles fixed by a binder of
resin or the like. One example of fixed abrasive pads comprises an
upper layer of abrasive particles fixed by a binder and a lower
layer of an elastic pad attached to the upper layer. Alternatively,
the fixed abrasive pad comprises abrasive particles fixed by an
elastic binder such as polyurethane.
Each of the transfer robots 4a, 4b has an articulated arm which is
bendable and extendable within a horizontal plane, and upper and
lower holding portions which are separately used as a dry finger
and a wet finger, respectively. Since two robots are used in this
embodiment, a first robot 4a is basically responsible for a region
from the inverters 5, 6 to the cassettes 2a, 2b, and a second robot
4b is basically responsible for a region from the inverters 5, 6 to
the polishing sections 1a, 1b.
The inverters 5, 6 serve to turn over a semiconductor wafer W, and
are disposed at positions that can be reached by the hands of the
transfer robots 4a, 4b. In this embodiment, the two inverters 5, 6
are separately utilized as a device for handling a dry
semiconductor wafer and a device for handling a wet semiconductor
wafer, respectively.
Each of the cleaning units 7a, 7b, 8a and 8b may be of any type.
For example, the cleaning units 7a, 7b near the polishing sections
1a, 1b are of a type that wipes both sides of a semiconductor wafer
with a roller equipped with a sponge, and the cleaning units 8a, 8b
near the cassettes 2a, 2b are of a type that holds an edge of a
semiconductor wafer and rotates the semiconductor wafer within a
horizontal plane while supplying a cleaning liquid to the
semiconductor wafer. The cleaning units 8a, 8b also serve as a
drier for centrifugally drying a semiconductor wafer. The cleaning
units 7a, 7b can perform a primary cleaning process of a
semiconductor wafer, and the cleaning units 8a, 8b can perform a
secondary cleaning process of a semiconductor wafer after the
primary cleaning process.
FIG. 4 is a vertical cross-sectional view showing a main part of
the polishing section 1a shown in FIGS. 2 and 3. Only the polishing
section 1a will be described below. However, the following
description can be applied to the polishing section 1b.
As shown in FIG. 4, polishing cloth 10 on the polishing table 11
has its upper surface serving as a polishing surface held in
sliding contact with a semiconductor wafer W as a workpiece to be
polished. The polishing table 11 is coupled to a motor (not shown)
disposed below the polishing table 11 via a table shaft 11a, so
that the polishing table 11 is rotatable about the table shaft 11a
in a direction indicated by arrow C in FIG. 4.
A polishing liquid supply nozzle 15 and a water supply nozzle 16
are disposed above the polishing table 11. A polishing liquid for
use during polishing is supplied onto the polishing cloth 10 from
the polishing liquid supply nozzle 15. A dressing liquid for use
during dressing, e.g., water, is supplied onto the polishing cloth
10 from the water supply nozzle 16. The polishing table 11 is
surrounded by a frame 17 for recovering polishing liquid and water
that have been supplied onto the polishing cloth 10. A tub 17a for
collecting and draining the polishing liquid and the water is
provided at a bottom of the frame 17.
The top ring unit 12 comprises a rotatable spindle 20, a swing arm
21 coupled to an upper end of the spindle 20, a top ring shaft 22
extended downwardly from a free end of the swing arm 21, and a
substantially disk-shaped top ring 23 coupled to a lower end of the
top ring shaft 22. When the swing arm 21 is swung by rotation of
the spindle 20, the top ring 23 is horizontally moved, and thus can
be reciprocated between the pusher 14 and a polishing position on
the polishing cloth 10, as indicated by arrow A in FIG. 2. Further,
the top ring 23 is coupled via the top ring shaft 22 to a motor
(rotating mechanism) and a lifting/lowering cylinder (both not
shown) provided within the swing arm 21, so that the top ring 23 is
vertically movable, as indicated by arrow D in FIG. 4, and is
rotatable about an axis of the top ring shaft 22, as indicated by
arrow E in FIG. 4. A semiconductor wafer W as a workpiece to be
polished is attracted to and held on a lower surface of the top
ring 23 by vacuum suction or the like. Thus, the top ring 23 can
rotate and press the semiconductor wafer W held on its lower
surface against the polishing cloth 10 at a desired pressure.
The dressing unit 13 serves to regenerate a surface of the
polishing cloth 10 that has been deteriorated as a result of a
polishing operation, and is disposed at a position opposite to the
top ring unit 12 with respect to a center of the polishing table
11. The dressing unit 13 comprises a rotatable spindle 30, a swing
arm 31 coupled to an upper end of the spindle 30, a dresser shaft
32 extended downwardly from a free end of the swing arm 31, and a
substantially disk-shaped dresser 33 coupled to a lower end of the
dresser shaft 32, similar to the case of the top ring unit 12. When
the swing arm 31 is swung by rotation of the spindle 30, the
dresser 33 is horizontally moved, and thus can be reciprocated
between a dressing position on the polishing cloth 10 and a standby
position which is positioned outside of the polishing table 11, as
indicated by arrow B in FIG. 2. Further, the dresser 33 is coupled
via the dresser shaft 32 to a motor (rotating mechanism) and a
lifting/lowering cylinder (both not shown) provided within the
swing arm 31, so that the dresser 33 is vertically movable, as
indicated by arrow F in FIG. 4, and is rotatable about the dresser
shaft 32, as indicated by arrow G in FIG. 4.
FIG. 5 is a schematic view showing a piping system of the dressing
unit 13 in the polishing section 1a shown in FIG. 4, and FIG. 6 is
a bottom view showing the dresser 33 shown in FIG. 4. In FIG. 5, a
portion of the dressing unit 13 is shown in cross section. As shown
in FIGS. 5 and 6, the dresser 33 has a plurality of dressing
elements 34 mounted on a lower surface of the dresser 33 for
dressing the polishing cloth 10 by sliding contact with the
polishing cloth 10. In this embodiment, each of the dressing
elements 34 comprises a diamond pellet made of diamond particles
electrodeposited on a disk, and a plurality of dressing elements 34
are mounted on the lower surface of the dresser 33. As shown in
FIG. 6, the dressing elements 34 are positioned along a
circumferential direction of the dresser 33 at predetermined
intervals, and thus annularly disposed on the lower surface of the
dresser 33 as a whole. The dresser 33 rotates and presses the
dressing elements 34 against the polishing cloth 10 at a desired
pressure to dress the polishing surface of the polishing cloth 10.
The dressing elements 34 may comprise a brush which has elongated
bristles such as nylon.
The dresser 33 has a plurality of ejection nozzles 35 provided on
its lower surface for ejecting a liquid in the form of a mixture of
a nitrogen gas and pure water as a cleaning liquid, toward a
polishing surface of the polishing cloth 10. As shown in FIGS. 5
and 6, the ejection nozzles 35 are disposed in an area surrounded
by the annularly disposed dressing elements 34, i.e., inside of the
dressing elements 34. The ejection nozzles 35 are radially
positioned around a center of the dresser 33. Each of the ejection
nozzles 35 is a nozzle directed toward an outer circumferential
edge of the dresser 33 so as to eject liquid toward the outer
circumferential edge of the dresser 33.
As shown in FIG. 5, nitrogen gas from a nitrogen gas source (gas
source) 40 and pure water from a pure water source (fluid source)
50 are supplied to the ejection nozzles 35 via a gas passage 41 and
a liquid passage 51, respectively. Pressure of nitrogen gas from
the nitrogen gas source 40 is regulated by a regulator 42. The
nitrogen gas is supplied to the ejection nozzles 35 via an
air-operated valve 43 and a rotary joint 60. Pressure of pure water
from the pure water source 50 is regulated by a regulator 52. The
pure water is supplied to the ejection nozzles 35 via an
air-operated valve 53 and the rotary joint 60. The gas passage 41
and the liquid passage 51 are joined to each other to mix the pure
water and the nitrogen gas at an upstream side of the ejection
nozzles 35. A mixture of the pure water and the nitrogen gas flows
into a passage 36 formed in the dresser 33 and is then supplied to
the ejection nozzles 35 via the passage 36.
The mixture of the nitrogen gas and the pure water is brought in as
liquid fine particles, solid fine particles as a result of
solidification of liquid, or gas as a result of vaporization of
liquid. To bring the mixture into these states is referred to as
atomization. An atomized mixture is ejected from the ejection
nozzles 35 toward the polishing table 11. Which state of the mixed
liquid to be ejected, i.e., the liquid fine particles, the solid
fine particles, or gas, is determined, for example, depending on
pressure or temperature of the nitrogen gas and/or the pure water,
or a shape of nozzles. Therefore, the state of the liquid to be
ejected can be varied, for example, by properly varying pressure or
temperature of the nitrogen gas and/or the pure water via a
regulator or the like, or by properly varying a shape of
nozzles.
FIG. 7A is an enlarged view showing one of the dressing elements 34
shown in FIG. 6, and FIG. 7B is a cross-sectional view taken along
a line of H--H in FIG. 7A. Each of the dressing elements 34 has a
large number of diamond particles electrodeposited on a lower
surface thereof. As shown in FIGS. 7A and 7B, the dressing element
34 has a vertical fluid flow hole 34a defined therethrough, and a
plurality of fluid ejection slots 34b defined in the lower surface
thereof. In this embodiment, as shown in FIG. 7A, the fluid
ejection slots 34b are extended from a lower end of the fluid flow
hole 34a toward an outer circumferential edge 33a of the dresser 33
and reach an outer circumferential edge of the dressing element 34.
An upper end of the fluid flow hole 34a communicates with the
passage 36 in the dresser 33. The mixture supplied from the passage
36 flows through the fluid flow hole 34a and the fluid ejection
slots 34b and then flows out of the dresser 33.
Operation of the polishing apparatus thus constructed for polishing
a semiconductor wafer W and dressing polishing cloth 10 will be
described below.
When a polishing process of a semiconductor wafer W is performed in
the polishing section 1a, the top ring 23 and the polishing table
11 are independently rotated, and a semiconductor wafer W held on
the top ring 23 and the polishing table 11 are relatively moved to
press the semiconductor wafer W held on a lower surface of the top
ring 23 against the polishing cloth 10 on the polishing table 11.
At this time, a polishing liquid is supplied from the polishing
liquid supply nozzle 15 onto the upper surface of the polishing
cloth 10. For example, a suspension of fine polishing particles of
silica or the like in an alkali solution is used as the polishing
liquid. Thus, the semiconductor wafer W is polished by a combined
effect of a chemical polishing effect attained by the alkali and a
mechanical polishing effect attained by the polishing particles.
The polishing liquid used during the polishing process is scattered
to an outside of the polishing table 11 by centrifugal force due to
rotation of the polishing table 11, and is recovered in the tub 17a
provided at the lower portion of the frame 17.
The polishing process of the semiconductor wafer W is completed
when the semiconductor wafer W is polished to a certain thickness.
At this time, properties of the polishing cloth 10 are changed due
to the polishing process, so that polishing performance for a
subsequent polishing process is deteriorated. Therefore, the
polishing cloth 10 is dressed by the dressing unit 13. During a
dressing process, the dresser 33 and the polishing table 11 are
independently rotated, and the dressing elements 34 mounted on the
dresser 33 are pressed against the polishing cloth 10 at a
predetermined pressure. At the same time that the dressing elements
34 are brought into contact with the polishing cloth 10 or before
the dressing elements 34 are brought into contact with the
polishing cloth 10, water is supplied from the water supply nozzle
16 onto the polishing cloth 10 to wash away used polishing liquid
that remains on the polishing cloth 10.
While the polishing cloth 10 is being dressed, the regulators 42,
52 and the air-operated valves 43, 53 are controlled to supply
nitrogen gas and pure water at predetermined pressures and
temperatures to the ejection nozzles 35 in the dresser 33 for
ejecting a mixture of the nitrogen gas and the pure water to the
polishing cloth 10. It is preferable to supply the nitrogen gas
under pressures ranging from 0.01 MPa to 0.7 MPa, and to supply the
pure water under pressures ranging from 0.1 MPa to 0.3 MPa. The
mixture is ejected in an atomized state onto the polishing cloth
10, scattering a portion of the dressing elements 34 that has come
off the dressing elements 34 in the dressing process toward the
outside of the dresser 33. At the same time, this ejected mixture
scatters polishing liquid and ground-off particles of the
semiconductor material remaining on the polishing cloth 10 toward
an exterior of dresser 33. Particularly, polishing liquid and
ground-off particles that have fallen into recesses in the
polishing cloth 10 can be blown away from the recesses by gas
contained in the mixture, and, further, can be washed away by
cleaning liquid (pure water). Thus, the polishing liquid and the
ground-off particles, which remain on the polishing cloth 10 to
cause a scratch, can effectively be removed from the polishing
cloth 10.
The mixture simultaneously flows from the passage 36 in the dresser
33 through the fluid flow hole 34a and the fluid ejection slots
34b, out of the dresser 33. Since the dresser 33 is rotated at this
time, the mixture is forced to flow out of the dresser 33 under
centrifugal forces. Therefore, the polishing cloth 10 is
effectively cleaned. Particularly, since the fluid ejection slots
34b are extended from the fluid flow hole 34a toward the outer
circumferential edge 33a of the dresser 33, as shown in FIG. 7A,
the mixture strongly flows out of the dresser 33. Hence, an effect
of cleaning of the polishing cloth 10 can be improved.
Water supplied onto the polishing cloth 10 and the mixture ejected
from the ejection nozzles 35 onto the polishing cloth 10 are
scattered from the polishing table 11 under centrifugal forces due
to rotation of the polishing table 11, and are collected by the tub
17a in the frame 17. After the dressing process, the dresser 33 is
returned to a standby position by the swing arm 31, and cleaned by
a dresser cleaning unit 18 (see FIG. 2) disposed at the standby
position.
In this embodiment, nitrogen gas is supplied from the gas source 40
to the ejection nozzles 35, and pure water is supplied as the
cleaning liquid from the fluid source 50 to the ejection nozzles
35. However, only a liquid (cleaning liquid) may be supplied from
the fluid source 50 to the ejection nozzles 35 without a gas being
supplied from the gas source 40. In this case, the regulator 52 in
the liquid passage 51 may be controlled to supply liquid (pure
water) at a high pressure to the ejection nozzles 35 for removing
polishing liquid and ground-off particles of semiconductor material
from recesses in the polishing cloth 10.
The ejection nozzles 35 in the lower surface of the dresser 33 are
not limited to the illustrated number and layout. The fluid flow
hole 34a and the fluid ejection slots 34b which are defined in the
dressing elements 34 are not limited to the illustrated positions
and shapes. For example, as shown in FIG. 8, the dressing element
34 may have a fluid flow hole 34a defined at a central portion
thereof and fluid ejection slots 34b defined therein at 90.degree.
intervals and extended radially outwardly from the fluid flow hole
34a. Further, in this embodiment, the dressing element 34 of the
dresser 33 comprises a diamond pellet. However, each of the
dressing elements 34 may comprise a brush.
Although certain preferred embodiments of the present invention
have been shown and described in detail, it should be understood
that various changes and modifications may be made therein without
departing from the scope of the appended claims.
* * * * *